ASGSB 1999 Annual Meeting Abstracts

EFFECTS OF MICROGRAVITY ON CARBOHYDRATE DEPOSITION IN ETIOLATED SOYBEAN SEEDLINGS. E.C. Stryjewski¹, K.M. Johnson², L.H. Levine¹, H.G. Levine1, V. Prima³, and W.C. Piastuch¹. ¹Dynamac Corp., NASA/KSC, FL, ²National Research Council, and ³Institute for Molecular Biology and Genetics, National Academy of Sciences, Ukraine.

Soybean seeds (Glycine max cv. McCall) were imbibed and germinated on orbit within NASA's Biological Research in Canister (BRIC) hardware as part of the CUE/GENEX spaceflight experiment (STS-87). Following landing, after having grown for 6 days in the spaceflight environment, etiolated seedlings were either (1) fixed for Schiff/PAS localization of starch, or (2) frozen for starch content assessment. Schiff/PAS staining showed that more starch was deposited in spaceflight grown seedlings than in the corresponding ground controls. Cross sections through various regions of the seedlings indicated that a majority of this additional starch was located in the elongated region of the hypocotyl where clusters of starch were evident in the endoderm and mesophyll. Preliminary determination of starch content indicated that starch concentration in this region nearly doubled in space. In contrast, the ground control plants were virtually devoid of these deposits. Longitudinal sections through the hypocotyl showed that starch in the ground control plants sedimented at the base of endodermal cells but appeared dispersed in the flight endodermis. However, starch grains in mesophyll tissues did not appear to sediment in either ground control or flight plants. These results suggest that starch functioned as a gravity sensing mechanism in the endoderm, but that starch deposited in the mesophyll did not have this role. We speculate that this gravisensing role led to the higher production of starch seen in the spaceflight samples. The presumed mechanism would relate to the reduced pressure these deposits would exert on the cell wall interior in the hypocotyl region (in space). This would delay the signal to stop depositing starch in the hypocotyl and result in additional deposits being laid down in a region not normally used as a carbohydrate sink.

(This work supported by NASA contract NAS10-12180 to the Dynamac Corp.)

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